1. Field of the Invention
The invention relates to an injector for a fuel injection system for internal combustion engines, having a pressure booster that has a first piston guided in a first guide bore and a second piston guided in a second guide bore, in which the first piston and the second piston define a pressure chamber that is under at least a supply pressure, and having a leaking oil line, the first piston being actuated by an actuator and the first piston at least indirectly actuating the final control element of a control valve, and to a fuel injection system for internal combustion engines using the injector.
2. Description of the Prior Art
To make it possible to assure a defined operating state of the injector and consequently good operating performance, and above all favorable engine starting performance, the second piston of the hydraulic pressure booster has until now been pressed against the final control element of the control valve by a spring, such as a cup spring.
This arrangement assures that the second piston of the hydraulic pressure booster will always assume a defined position, but air inclusions or the like can have the effect that a defined operating state of the injector is still lacking, and in particular that the engine starting performance is inadequate.
The primary object of the invention is to furnish an injector for a fuel injection system for internal combustion engines that has a pressure booster with improved operating performance.
This object is attained according to the invention by an injector for a fuel injection system for internal combustion engines, having a pressure booster that has a first piston guided in a first guide bore and a second piston guided in a second guide bore, wherein the first piston and the second piston define a pressure chamber that is under at least a supply pressure, and having a leaking oil line, wherein the first piston is actuated by an actuator and the first piston at least indirectly actuates the final control element of a control valve, in which the second guide bore communicates hydraulically with the leaking oil return and the pressure p1 in the leaking oil return is lower than the supply pressure.
As a result of the prevailing pressure difference between the pressure chamber and the leaking oil return, a hydraulic force that presses the second piston against the final control element of the control valve always acts on the second piston.
As a result, not only is a defined position of the second piston of the hydraulic pressure booster assured, but in addition, there is a constant exchange of the fuel, or possible air inclusions, in the pressure booster.
Because of the low pressure level in the injector directly downstream of the control valve, the operating performance of the outlet throttle disposed between the control chamber and the control valve also improves.
In variants of the invention, the first guide bore, the first piston and the housing are sealed off from their surroundings, in particular by a bellows, so that no leakage can occur, and the supply pressure in the pressure chamber remains high.
Further in the invention, it is provided that supply pressure in the pressure chamber is furnished by a supply line discharging into the chamber formed by the housing, bellows and first piston, so that all the lines (31, 25, 27) and chambers (34, 17, 29) always have a flow of fuel through them.
In a further feature of the invention, a pressure holding valve is disposed in the supply line, so that pressure p2 in the supply line is limited, in particular to 50 bar.
Another embodiment has a recess which is in communication with the leaking oil return at the second guide bore, so that the control and leakage quantities can be returned without problems.
In a further variant of the invention, the second piston actuates the final control element of the control valve via a tappet, so that the portions of the second guide bore that lead between the second piston and the tappet need not be precisely aligned, and different tolerances are possible.
Further in the invention, the outlet side of the control valve discharges into the leaking oil return, so that the control quantity is carried away.
In another feature of the invention, the actuator is a piezoelectric actuator, thus making major control forces available.
Another embodiment provides for mounting the housing, the control valve, and the actuator in a retaining body, thus on the one hand facilitating manufacture and mounting and on the other making a play-free, prestressed connection of the components possible.
The object stated above is also attained by a fuel injection system for internal combustion engines, having a high-pressure fuel pump, having a high pressure fuel reservoir, and having at least one injector according to the invention, so that the advantages of the invention come into play in this fuel injection system as well.